package uk.ac.strath.cis.metric_spaces.distance;

import uk.ac.strath.cis.metric_spaces.framework.Distance;

public class LevenshteinDistance implements Distance<String> {

    private int minimum(int a, int b, int c) {
        return Math.min(Math.min(a, b), c);
    }

    /* (non-Javadoc)
     * @see uk.ac.strath.cis.rmoss.metric_spaces.framework.Distance#distance(java.lang.Object, java.lang.Object)
     */
    public double distance(String str1, String str2) {
        int[][] distance = new int[str1.length() + 1][str2.length() + 1];

        for (int i = 0; i <= str1.length(); i++) {
            distance[i][0] = i;
        }
        for (int j = 0; j <= str2.length(); j++) {
            distance[0][j] = j;
        }

        for (int i = 1; i <= str1.length(); i++) {
            for (int j = 1; j <= str2.length(); j++) {
                distance[i][j] = minimum(
                        distance[i - 1][j] + 1,
                        distance[i][j - 1] + 1,
                        distance[i - 1][j - 1]
                                + ((str1.charAt(i - 1) == str2.charAt(j - 1)) ? 0
                                        : 1));
            }
        }

        return distance[str1.length()][str2.length()];
    }

}
